Scientific name: Leptocorisa acuta (Thunberg), L. oratorius (Fabricius), and L. chinensis Dallas

Common name: Slender rice bugs

Deformed and spotty grains caused by feeding of rice bugs during hard dough stage of the rice plant Dark grains caused by infection due to bacteria transmitted during feeding of rice bugs The slender rice bug Leptocorisa sp. Ventral abdomens of two common species of rice bugs Leptocorisa oratorius (Fabricius) and Leptocorisa acuta (Thunberg) A stylet sheath secreted by the rice bug to enable its mouthpart during feeding Brown eggs of rice bug Slender and green nymph of rice bug Nymph of rice bug

Taxonomy:

Economic importance

Both the adults and nymphs feed on grains at the milking stage. They are a serious pest of rice and can reduce yield by as much as 30%.

Geographical distribution

Australia, Bhutan, China, Fiji, India, Indonesia (including New Guinea), Malaysia, Mauritius, Myanmar, New Caledonia, Papua New Guinea, Philippines, Samoa, Sri Lanka, Taiwan, Thailand, Tonga, and Vietnam.

Morphology

Egg
The eggs are oval, shiny, and reddish brown. They are laid in batches of 10-20 in one to three rows along the midrib on the upper surface of the leaf. 

Nymph
The insect passes through five nymphal instars. The younger instars are pale in color. The nymphs have long antennae. The older instars measure 1.8-6.2 mm long. They are yellowish green. 

Adult
All the adults of the three species of rice bugs are slender and light brown. The largest of the species is L. oratorius, measuring 19 mm long with distinct ventrolateral spots on the abdomen. L. chinensis has a body length of 17.5 mm with a dark brown antennal base and lateral black lines on the prothorax. The smallest species is L. acuta, 16 mm long. It has no other distinguishing characteristics.

Symptoms

Feeding causes empty or small grains during the milking stage. At the soft or hard dough stage, feeding causes deformed or spotty grains. The grains become dark as a result of spilling of endosperm. The spillage becomes a medium for fungal infection.

Biology and ecology

The female adults lay their eggs on the foliage or on dead parts of the leaves and stems. Egg incubation is 5-9 days depending on the temperature. 

The nymphs pass through five nymphal stages in 17-26 days. The nymphal stages are not easily distinguished because of their green color; however, their sizes vary. 

Adults live until 69 days. They are active during the late afternoon and early morning. Under bright sunlight, they hide in grassy areas. They are less active during the dry season. In cooler areas, the adults undergo aestivation or diapause in grasses. On emergence, they feed on the wild host for one to two generations before migrating into the rice field at the flowering stage.

Host range

The primary hosts of the rice bug are rice and Echinochloa sp. The secondary hosts are Alloteropsis cimicina (L.) Stapf, Artocarpus sp. (breadfruit), Bothriochloa pertusa (L.) A. Camus, Brachiaria miliiformis (Presl) A. Chase, B. mutica (Forssk.) Stapf, Camellia sinensis (L.) O. Ktze. (tea), Chloris barbata Sw., Dactyloctenium aegyptium (L.) Willd., Dicanthelium clandestinum L., Eleusine indica (L.) Gaertn., Mangifera indica L. (mango), Myristica sp. (nutmeg), Panicum miliaceum L. (millet), P. repens L., Paspalidium (Burm.) A. Camus, Phaseolus sp. (beans), P. maximum Jacq., Psidium guajava L. (guava), and Setaria glauca (L.) R. Br.

Detection and inspection

The pungent odor of the rice bug signifies its presence. Its slender and elongated body can identify the insect. When disturbed, the nymphs drop to the lower part of the plants and the adults fly within a short distance.

Management

Cultural control
Removal of alternate hosts such as grasses on bunds, early planting, and the use of late-maturing cultivars can reduce feeding damage of the rice bug.

Biological control
Eggs are parasitized by Gryon nixoni (Masner) and Ooencyrtus malayensis Ferriere. They are preyed upon by Conocephalus longipennis (de Haan). Both the adults and nymphs are hosts to Euagoras sp., Micraspis discolor (Fabricius), and Neurothemis terminata terminata Ris. The fungus Beauveria bassiana (Balsamo) Vuillemin infects both nymphs and adults.

Host-plant resistance
Coarse-grain and bearded cultivars are resistant to the rice bug. In India, Sathi, Soma, Mundagaketty, W1263, CR44-82, Badshabhong, Hamas, and CR44-35 are resistant to the rice bug.

Selected references

Ahmad Y, Balasubramaniam A. 1976. Major crop pests in peninsular Malaysia. Ministry of Agriculture, Malaysia.

Akhbar SS. 1958. The morphology and life history of Leptocorisa varnicornis Fabr. (Coreidae: Hemiptera): a pest of paddy crop in India. Publ. Aligarh Muslim Univ. Pub (Zool.Ser) Ind. Ins. Typ. 5:1-50.

Corbett GH. 1930. The bionomics and control of Leptocorisa acuta (Thunberg) with notes on Leptocorisa spp. Malaya Dept. Agric. S.S. and F.M.S. Sci. Ser. 4:1-40.

Kalshoven LGE. 1981. Pests of crops in Indonesia. Van der Laan PA, Rothschild GLH, translators. PT. Ichtiar Baru - Van Hoeve, Jakarta. 701 p.

Rajapakse RHS, Kulasekera VL. 1980. Survival of rice bug Leptocorisa oratorius (Fabricius) on graminaceous weeds during the fallow period between rice cropping in Sri Lanka. Int. Rice Res. Newsl. 5(5):18.

Reissig WH, Heinrichs EA, Litsinger JA, Moody K, Fiedler L, Mew TW, Barrion AT. 1986. Illustrated guide to integrated pest management in rice in tropical Asia. Manila (Philippines): International Rice Research Institute. 411 p.